How should I handle IDs like ClientId, MessageId, DSId, and CorrelationId in NeoLoad?

The underlying protocol used for Flex application is AMF (Action Message Format). It is a binary protocol.

When recording a Flex application NeoLoad deserializes the binary stream between the browser and the server. It will convert the binary data to XML content. These IDs are used by the AMF protocol. In fact, there is no need to handle them with Variable Extractors as it is automatically handled by NeoLoad.

You can let the hardcoded values remain, during replay they will be replaced automatically.